1. Field of the Invention
The present invention relates, in general, to the technical field of security systems and, in particular, relates to a sensor embedded in a layer of cement material.
2. Description of the Related Art
As is known, there has been a long felt need for protection along the perimeters of locations. Such protection immediately signals, by means of a special alarm emission, any attempt to enter a place to be protected or any attempt to escape from said place.
Well-known and widely used security systems, called underground systems, use various types of sensors intended to be placed in the ground or embedded in the pavement along the perimeter of the place to be protected or along potential accesses to said place. In practice, the underground system sensors are generally sensitive to the footsteps on the ground or on the pavement of a person approaching the perimeter or protected area.
A particular security system of the type described above is known from the teachings of the European patent EP 1005003 B1, which in particular discloses a security system including a plurality of pressure sensors fitted with piezoelectric transducers and intended to be embedded in the pavement. Said sensors are such as to perceive any microstress occurring in the cement layer forming the pavement caused as a result of a person walking on said pavement.
It has been observed that the sensitivity of the security systems known in the art which use pressure sensors intended to be embedded in the pavement, as for example the security system described in the above-mentioned patent EP 1005003 B1, is strongly influenced by the ambient temperature. In particular, it has been observed that the sensitivity of said systems increases as the ambient temperature increases, so that if the security system is calibrated to work at a certain average temperature, the sensitivity of the system will be either too high or too low as the temperature moves away from said average temperature. This situation can create drawbacks and risks because if, for example, the sensitivity of the system is too high, ambient disturbances, such as the passage of a small animal, can generate false alarms. On the contrary, if the sensitivity is too low, there is the risk that dangerous intrusions may go undetected.